Multiple possibilities:
1) You did not actually have the virus enter you even though you were exposed to it, therefore could not have been infected.
2) Your previous immunity allowed your immune system to immediately recognize it and you were immune.
3) You did get infected but it was very mild or asymptomatic as your immune system was able to counter the infection faster due to exposure to a similar virus
It face to face contact with no precautions for hours at a time as I helped around the house when my friend was recovering at home and I drank out of the same coffee cup. So 1 ain’t it.
2 or 3 had to be it.