The article said the tip was that he was attempting to buy illegal magazines. That is enough for a law enforcement to open an investigation.
It says he was charged with possessing the magazines so I think they must have had an actual crime to charge him with in the end.
The real question in the trial will be how did they get from the initial tip to finding the illegal magazines and was it justified. The officers got a search warrant so they went through the proper process. This would then put the decision on the judge who signed off on the search warrant. Depending on how strong the case there are definitely a couple of points his defense attorney could attack.
They got a "tip" like how for 2.5 years the fake news said "credible source" for Russian collusion. I wanna see who gave that tip, if anything, it would have to be someone he knows or has a relationship with (friends, family, classmates, forum SN's, etc...) $20 says it was an annonomist call to 911.
So even if the "tip" was bogus, he still is arrested and his property taken. It will cost him money to defend himself and to get any guns back. Also he was expelled from school too right? So either way, he's screwed for the rest of his life. But also, he should not have done anything illegal, like purchase standard capacity magazines. He knew the law and broke it. Regardless of how he got caught, it opened the door.
But in the end, the mags don't matter, it all started with the meme and red flag law. PD got lucky when they searched his home and needs a story to cover themselves. Like I said, all my sources state red flag and not that a tip was given or he tried to buy standard capacity mags. And I have more trust in my intel than the mainstream media.