Can you seriously „overlook“ a message?

There was a guy, a former coworker, I really liked. We got along well. So one day I saw that he got promoted, which is a big deal. Two months earlier we had met for coffee, so wer still on a friendly basis even though we don’t work together anymore. For his promotion I quickly congratulated via WhatsApp-Message because I still have his number. And in the same month he congratulated me for my birthday also over WA. He didn’t answer, no „thank you“ or anything. For almost three months I thought that he must be ignoring me for whatever reason. I deleted his number after that, I thought it was so rude. Now, a few days ago, he messaged me „ohh man. I just saw your message. Thanks a lot“ (and a lot of emojis. And then sent another message asking about the job. I personally think he just looked up my name in his contacts, because he wanted to ask me something and then saw that he didn’t reply.

Because, seriously, how can you overlook a message for three months?

Even if he did, he seems to not care about me at all!

I only replied to his question regarding the job. I didn’t reply to just first message at all, makes me look even more stupid.

How do you guys see this? Is it really possible?