I busted someone in an earlier session of 2NL when they jammed 77 vs my QQ and took a 150BB stack from them. Later when I was reviewing my session in HEM and it said the $EV difference was -$1.01. How is this possible? Wouldn't getting it all in with a bigger pocket pair be +EV?

Hand went as follows:

***** Hand History for Game 14701760270 *****
$0.01/$0.02 USD NL Texas Hold'em
Seat 4 is the button
Total number of players : 6/6
Seat 4: Hero ( $2.76 USD )
Seat 2: xx ( $4.74 USD )
Seat 5: Villain ( $2.77 USD )
Seat 3: xx ( $2.25 USD )
Seat 1: xx ( $2.60 USD )
Seat 6: xx ( $1.98 USD )
Villain posts small blind [$0.01 USD].
xx posts big blind [$0.02 USD].
** Dealing down cards **
Dealt to Hero [ Qc Qh ]
xx calls [$0.02 USD]
xx folds
xx calls [$0.02 USD]
Hero raises [$0.12 USD]
Villain raises [$0.43 USD]
xx folds
xx folds
xx folds
Hero raises [$1.40 USD]
Villain is all-In [$2.33 USD]
Hero is all-In [$1.24 USD]
** Dealing Flop ** [ 5d, Kh, 9s ]
** Dealing Turn ** [ 2h ]
** Dealing River ** [ Kc ]
Hero shows [ Qc, Qh ]two pairs, Kings and Queens.
Villain shows [ 7h, 7d ]two pairs, Kings and Sevens.
CleanoutKid wins $5.31 USD from the main pot with two pairs, Kings and Queens.

You have an EV of x. The result is y. EV difference is z. z = x - z

Let's say your EV is 1 and the result is either -2 for a loss or +2 for a win.

z = 1 - 2 = -1 difference for when you win

z = 1 - - 2 = +2 for when you lose

QdQh vs 7d7h is 81.592% to 18.408% in hand equity.
It is easy to see what you should expect back from this pot in the long run it is Hand Equity x Pot Size. (This is ignoring the rake)
Assuming the final contested pot was $5.31 and if you played out this hand millions of times you would expect to get back on average 0.81592 * $5.31 = $4.3325352

In the actual hand you had some luck and won (you could have lost) so you got back $5.31. HEM is telling you that for this hand your difference from expected is -$1.01, I get a result of ($4.3325352 - $5.31) = -$0.9774648 but this minor diff is probably due to how the rake was handled in the calculation.

Edit: actually the first hand was QcQh so the hand equity was 80.925
0.80925 * 5.31 = 4.2971175 and the diff is $4.2971175 - $5.31 = -$1.0128825

So you owe $1.0128825 to the god of variance but luckily for you this god has a worse memory than the proverbial goldfish and will never ask for it back.

You got it in with about 80% equity. You won 100% of the pot.
Since you won more than expected (you won a $5.30 pot instead of about $4.25), the stat kind of tells you how much to add (or in this case subtract) to your actual net $ to see your expectation. In the stats page in HEM it will show up as a negative number when you win, which is confusing, I have to say. On your graph, your orange line and green line would both have moved up, but the orange line will have gone up by $1.01 less than the green one.

It's a counter-intuitive (and not very useful) stat for sure. Add the EVbb/100 stat to your reports if it's easier to think of "What I 'should' have won".

So basically its -EV because I won more than I should have and not because I should have lost money? If that's the case though wouldn't it be a smaller positive number?

The math has already been provided. Actual win $5.31, expected win $4.30. EV differential = $1.01

It was a 265bb pot. That's pretty big. Winning about 20% more of it than expected is going to be a "lot" of money.

Oh ok I think I get it now, what a misleading stat lol

I thought this meant that I made an actual mistake I was unaware of