Catching flake for my junior being offline during WFH days, what can I do?

I'm not his manager so I'm not sure why is it my fault. I'm a senior dev and I have a junior whom I mentor and guide. He's a really great guy and works hard so when he asked if he could WFH everyday,

I'm not his manager so I'm not sure why is it my fault. I'm a senior dev and I have a junior whom I mentor and guide. He's a really great guy and works hard so when he asked if he could WFH everyday, I said "sure but don't get caught and come up with an excuse if you do". Months went by and he's been logging off earlier than usual lately like say 2-3pm instead. Apparently HR asked him and he specifically said "oh my manager said it was ok" so now I'm fucked but like I said... I'm not his manager lol but for some reason they pin this shit on me. What can I do about this? Honestly it's not my fault, he does more work than the bozos who come in office everyday, HR is just being stupid. I got a interview lined up and I'm 3 rounds deep, I'm pretty sure I'll get an offer, should I just bail? Edit: Welp, unfortunately this blew out of proportion before I could even respond to HR. I'm getting laid off next Monday for violating company policies. Good news is the junior is fine, thank god, he's a nice guy and works hard so if anyone's to blame, it's me. I messed up as his mentor, oh well. Thanks for all the help, I'm a little bummed out and tbh I feel betrayed but it is what it is.