My drain valve had recently broke off and when i saw a plumber in a store he was like thats know to happenand told me to cap it off. In which i did. I’m a single parent so i was listening doing what was easiest and cheapest for me yet i noticed a lil smoke coming from where i capped it and yes it scared tf out of me so i turned the gas back off. I have been looking for answers trying to see if that was just normal do to everything that occurred. Any insight would be extremely appreciated. I’m hoping it was just steam for the gas being on drying up what water was still there. TIA

burning gas makes no smoke. unless the air adjustment was so far out of whack that the flame was bright yellow and creating black sooty smoke.
there should be an observation (glass like) window so you can see the flame.
as for your repair, I can't say much except it may have a tiny leak inside that may be getting hot enough to make steam ??

I would recommend calling out a plumber to do onsite check up.