Reading between the lines, this suggests that they've decided to use an external firm to cover these security domains (for now). Without knowing which firm or firms we obviously can't say anything specific about their reputations, but I will say that I know some individuals who operate in this space and there are some very qualified and talented outside security firms out there.
However, the good firms aren't cheap. Obviously we can't know the details, but I wouldn't assume this move was motivated by cost-cutting reasons. Keeping a top-notch outside security firm fully involved could easily cost more than the salaries of the people who were let go.
I don't want to single anyone out, but a quick glance through LinkedIn leaves me somewhat confused about their former security team's structure. I could be missing something, but the only lead I found on LinkedIn was listed as "acting head of security" with a description that they were covering the Head of Security position for now. It's possible that the security team were good engineers, but maybe not the exact engineers/managers that Patreon needed at this stage of their development. Some times a mismatch like that really can't be overcome easily, so employing a known external firm can cover the gaps while the company tries to find a better match for their security leadership needs internally (if they return to internal at all).
This move could make even more sense if Patreon was aggressively heading toward IPO. In this case, the company would need to demonstrate that they've done their due diligence and made a best effort to cover security as best they can, even if that means paying exorbitantly for an external firm that has helped prepare companies for IPO in the past. If their internal security team didn't have this experience (and maybe didn't even have an official head of security) then they didn't stand a chance.