I feel like him using the excuse of everything being in lockdown and he was not able to get a ring would be absolutely ridiculous. I feel like a man/woman who is thinking of proposing to someone else would pick out a ring in advance. Many people I knew had a ring for about a year, when they realised the person is the one and just kept it until the right time to propose. Plus you can still buy it online!!! It's not as personal, I admit but if you were desperate you would do it. Considering the amount of crap he buys off the internet, a package for him wouldn't make Zoey wonder what it is. You can always ask people especially on websites like that to package it in a neutral packaging so no one can tell the company it came from!!!
Edit: Plus he always said online that he can't buy a ring from a shop cause people would recognize him and ruin the surprise so probably IF he wanted to do it would have customised/bought one online way in advance of her birthday
Actually curious what she gets from him