Just got an oil change, now need new O2 sensor?!

Hey everyone I hope I can get some help.

99 Civic EX
242, 065mi

I just came back from getting an oil change, and as I was driving home my check engine light came on so I drove back to the place. Turns out the O2 sensor next to the oil filter needs to be changed? Thing is, my mom told me that we had just changed that part in order to pass the smog test to register the car last year. We bought the part from Honda I believe but I think my mom's boyfriend had changed it. Honestly I'm slightly iffy about his car skills.
Note: I recently had my oil cap fall off, so there is oil all over the engine/hood that I'm cleaning in a couple days.

Could it have been put in wrong? Or could the guys that changed my oil mess with it while changing my oil? They claimed it was old and needed to be changed.

don't ever go back to that garage again...

take it to autozone, have them read the trouble code and erase it to see if the check engine lights up and spits out the same code

make sure you check the plug to the o2 sensor to see if they didn't unplugged it

Trust me, I won't be going anymore. I had also done an alignment with them before and it wasn't done correctly at all. They turned off the light and it hasn't gone off again, we also washed the oil off the engine. I'll do what you said and make sure they didn't disconnect anything. Thank you so much!