Topics: Multiple entry tourist visa, USED-Stamp

Hi i am curious if anybody experienced this or knows if there are problems

the last time i did enter Thailand at don muang an officier (maybe he has mistaken it for a single entry) stamped a used on my visa. He didn´t say anything nor did he ask questions. I saw this stamp when checking the entry stamp, which was fine, 60 days, normal. Behind the row of queued counters there was a single counter without queue i asked for advice she took pictures of the passport id site and visa put the information in the computer wrote this in Thai on it (translates to something like this is an multiple entry visa)

I am will be making a trip in Vietnam, should i do anything before leaving Thailand or other advices for me ?