Tumblr pic message

So I'm not really sure how tumblr works never really had an account but my fiance does and when he first got together he told me he used it for his porn site? OK np didn't think twice about it not gonna stop you from watching or looking at porn as long as you don't chose porn over me. So earlier today we were listening to music on his phone and we paused it to talk and when the CONVO was over I unlocked his phone and saw a tumblr notification and scrolled down and it was a message from some chick with a pic of her vagina and ass and she was bending over.... I didn't say anything because we were in the car with his fam when it happened and didn't wanna talk about it in front of his mom and sister so I just put his phone done and zoned out.. for those of you who have been in this situation or have a tumblr is it normal to just get random pics like that or is it something that he would of asked for first? And no I cant go thru his phone he keeps it on him at all times??? Plz help here

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