awkward story

I went into the SWKT the other day (ps...my dad claims he named it that) excited to work on a homework assignment. I went down to the open labs where I've gone many times before. Set my stuff down, used the restroom, (tmi?...I told you it was an awkward story) and came back to my computer. Started doing my assignment. Suddenly a professor stands up, and says,
"okay class, let's get started"
ahhhh I was in a class.
They opened up an excel sheet and started going.
I had two options, walk out now and just feel strange or grin and bear it.
I grinned, and enjoyed the class.
I finished my assignment, shopped a bit online and occasionally looked up at the teacher to nod like I knew what was going on. He appreciated it. I could tell.
When he said to "pull our your books and do a problem on your own" I pretended to open my book and look very interested. I was secretly terrified he would come back and see I was looking at a book about the appropriate ways to teach children. But he did not.
I left at 2:53. I'm not sure if the class was over but I had class at 3.
What a silly experience.