I am not quite aware what the reason for the ban was (most likely spamming), but you friend should be more careful, to avoid subsequent temporary bans and maybe a permanent one.
Here's a little explanation of how the mod gives the user a ban
[temporary - permanent]. The OP should know about this, and tell his friend not to post anywhere else with his alt account other than in meta. If his friend ignored him, then it was clear that it was a ban evasion
[if catch]. Staff do not want to hand out bans for unconstructive posts but if we feel that you as a user are continually making very poor or unsubstantial posts due to your paid signature the following bans will be issued:
First offence: 7 days
Second offence: 14 days
Third offence: 30 days
Fourth: Permanent ban
Your first ban is your first warning. If you have to be banned for a fourth time it is permanent and you will no longer be allowed to participate on the forum under any accounts. Note: If you are banned on one account then you are not allowed to post under any accounts you own for the duration of your ban. The only exception to this rule is Meta where you can discuss the circumstances of your ban if you wish to do so but anywhere outside of that sub will be considered ban evasion and will get your ban doubled, but it is generally best to just patiently wait out your ban and improve your posts on return and hopefully no further bans will be needed.
Usually temporary bans are shared due to spamming, but I don't see that the user gets more than one post deleted so far on a bpip basis. There must be another reason why it's banned, but spamming is most likely.