Thick booger-like white substance during sex

So yesterday me and my boyfriend had unprotected sex. He was doing it from behind and I was bent over, yesterday was the first day of my ovulation window according to this app and when he pulled out at a certain point to adjust ourselves. We noticed a thick white substance sitting on the tip and sides of his penis. It didn't look disturbed at all and it was just sitting very neatly on it, he said that he didn't cum. And his penis was still hard, plus I WAS aroused however I haven't experienced orgasming during sex yet so it scared me at first. (Note that I've actually never had sex during my fertile week) We wiped off the substance with tissue and it seemed to have matched the color of my discharge on my panty liner prior to having sex. Afterwards we kept on and THEN he pulled out and ejaculated a minute later, in comparison his cum was more liquidy/runny and not as white and thick as the substance earlier. Just wondering if anyone has any idea what this is and if I should be worried? I've read about "creaming" and cervical mucus but please feel free to leave an input. Thanks guys for reading!