Only reads I have is that villain is a 3-4 tabeling reg at 7$ turbos, has big preflop leaks, not very aggro and his ranges seems value heavy in most spots (I only have 100 hands against him). I also think he is only bluffing with high equity hands like FD and GS+ 2 overcards here.

I usually fold this to a larger size like 75% pot, but I think I made a mistake and folded to 50% pot. How light are you calling this turn?
BTW I think hands like 86o and 96o is better to call than J7.

PokerStars - $6.71+$0.29|10/20 NL (2 max) - Holdem - 2 players
Hand converted by PokerTracker 4

Hero (BB): 79 BB
SB: 71 BB

SB posts SB 0.5 BB, Hero posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 7 J

SB raises to 2 BB, Hero calls 1 BB

Flop: (4 BB, 2 players) 6 A 7
Hero checks, SB bets 3 BB, Hero calls 3 BB

Turn: (10 BB, 2 players) 5
Hero checks, SB bets 5 BB, fold

Call turn and re evaluate river for any bet that is <= 50% of pot.
Fold to >50% pot bet... IMO

I think that 86o,97o and J7o fall into the same category of hands for calling preflop in heads up!
Imo is more preferable to call a raise OOP in HU with a hands like K9 than A2.A2 might be better equity wise but i prefer calling with a hand that can flop decent pairs with decent kickers than an A with a crappy kicker cause if villain applies a lot of pressure I won't know where i stand most of the times.
Now for the hand you should have called.He is barreling a hyge part of his range consisting of pair pairs+FD's and his FD's on the turn.
I think calling this small bet OTR and reevaluating river is a good way to approach the hand.Most of the times when the river bricks of he will shut down.
Note tha he is multitabling too and might be playing autopilot!

You say : his ranges seems value heavy in most spots (I only have 100 hands against him). I also think he is only bluffing with high equity hands like FD and GS+ 2 overcards here.

I generally take notes to take borderline decisions like this, and here with this kind of note, I don't mind folding, really.