I wouldn't say it's WRONG.
For example, in any case where a host has multiple names, the IP address can ONLY map-back to ONE name. Is it "wrong" that the other names don't have a reverse back to them?
If you hosting on a shared IP, you CAN'T reverse-map to your domain. The IP will map back to a name belonging to your hosting company. This is also common in the case of non-shared IPs. Some hosts will map to your name, others won't.
I'm ambivilent on the issue. While it "looks better" if it maps back to your domain name, by mapping to the host you show you are "playing by the rules". If you don't actually own the server, hosted in your own facility, I think that mapping the IP to your domain name suggests some attempt at evasion. It suggests that you are trying to hide who your hosting company is - perhaps to avoid DMCA requests to your host, legal process, etc.
The one common case where reverse-mapping is important is in the case of SMTP servers. A good reason why most people shouldn't run their own. For anti-spam reasons, many SMTP servers (or other mail delivery agents) will not pass mail to other SMTP servers that don't reverse-map back to the name given in the MX record.
If you do want to run your own SMTP server, put it on a dedicated IP address, and make sure you can set-up the reverse to point to the name used in the MX record. Or, if you do share the IP with a website, make sure the reverse points to the MX name, not the website name. (Or make the names the same.)
But you've got a bigger problem. You used a PTR record to point to a name for which there is no A record. Not sure why there isn't an A record (ask your host) but the easy quick-fix is to use an A record rather than a PTR record. Also, note, you CANNOT use a PTR record for the base domain name, in any case. (Some systems may ALLOW you to do this, but it is WRONG and WILL NOT WORK CONSISTENTLY.)
www.example.com PTR example2.com OK
example.com PTR example2.com NO
The first example will work, but only if example2.com has an A record.
Just use an A record with www.example.com and example.com in the above examples. This has the added advantage of being slightly faster due to one less DNS lookup.