Husband getting "spam" messages from Instagram

So this is just a general question yes or no.... Today I decided to play a game on my husband's phone & then I went to his Instagram account to look at the pictures he posted for our vacation & noticed that he had a message from a chick asking to send dirty pics if he signs up. Should I be mad or just let it roll off my back?.... Is there a way to look at archived messages.. I don't have a Instagram, only Facebook, but notice that he uses his Instagram account more. Sn: he follows lots of nude girls.....