These kinds of repeat suspensions are very common in cases like this. Here’s how and why that can happen:
When people report an account for spam, Twitter mostly ignores the report UNLESS the person reporting has received the spam they are complaining about. This way, hundreds of people can’t band together and report an account for spam to try to get it suspended. Twitter’s automated systems mostly only “listens” to spam reports from people actually receiving spam from the account.
The way it works, as explained here, is if the two accounts have no relationship (the person receiving the “spam” didn’t contact the sender first; neither accounts follow the other) Twitter treats those reports very seriously, and will auto-suspend the account for sending “multiple unsolicited mentions” IF there are enough spam reports close together.
But in most cases like this, a second suspension happens closely after the first (if the account owner reinstates the account).
The reason is that once an account has been suspended once, Twitter’s automatic system makes it vulnerable to being suspended again if there are more spam reports, even if they are from people NOT receiving spam, as explained here.
So @FiredBigBird fell victim to the classic “double suspension” that happens to accounts that include usernames of people they have no relationship with, when those people don’t like what is being said.