Quick past subjunctive question

[rparmst]

I was saying something to a friend who is Dominican and Puerto Rican yesterday, and he corrected me, but was not able to explain why. i thought I had been doing pretty well with subjunctive until his correction:

I said, "Cuando llegué, me sorprendió que las personas en el gimnasio no tuvieran cuadrito."

He said that i shoud use tenían, not tuvieran. I know he didn't misunderstand and think I said tuvieron because it was via text, and I also asked him about that... I thought that following verbs of emotion like sorprender, subjunctive is used. Could someone please clarify? (I do realize that is is rude to talk about people's lack of 6-pack abs )