At my local casino i was playing 21, a variant of BJ. only difference is: you lose at stand off.

Also there is a 5 card bonus, if you get 5 cards and hold 21 or lower you will get your bet and still are in the race to win the hand against the dealer.

Let's say i was playing 10$ a hand.

I get a total of 4 cards, giving me a soft 18. I was drunk and blind on the 4 cards (trying to get the 5 card bonus) so i said hit, the whole table frowned at me for hitting while holding 18 ( even the dealer).

Next day i was thinking my play was actually good because with soft 18 at 4 cards i will 100% get the 5card bonus of 1 bet ( 10$ in this case) and STILL be in the race for antoher potential 10$ win against the dealer.

Was this the right play, having in mind the rules and bonus at my casino?

I'd have to actually run the numbers to say conclusively, but I'm almost certain your play is correct. Soft 18 is actually a pretty garbage hand, and as you explain it taking a card would essentially guarantee you a push at worst, and function almost like doubling down for free at best (bet $10, win $20) I'd be praying for this chance against a dealer 7.

Depending on the dealer's up card, it could have been correct to hit no matter what. Basic strategy says you hit s18 vs 9/10/A.

Sounds closer to pontoon than blackjack.

Basic strategy is dependent on the rules, which means "basic strategy" you find for a regular shoe game will be incorrect for a game with bonus pays. Some rules make almost no difference, some have an enormous impact. It's part of the reason most players concede a HUGE edge to Spanish 21.

For example, say you're playing in a game where hitting to 21 pays 3:1 automatically, except on doubled or split hands. What's your play on 11 vs 6? Standard double, right? Except now it's a colossal blunder. Why risk twice as much money to get paid even money when you can just take a card and get paid more in the first place?

That's similar to what OP is facing. Unbreakable hand, guaranteed a push at worst by taking a card, still in the running to win as well. I'm actually sure there would be scenarios like AA27 vs 4/5/6 where playing it as an 11 and taking a card is the right choice, since you can't lose.