IIRC Microsoft does share malware detection information with other antivirus providers, so that sounds plausible. (I think that's also part of the reason why W

IIRC Microsoft does share malware detection information with other antivirus providers, so that sounds plausible. (I think that's also part of the reason why Windows Defender appears less competitive in antivirus comparisons, since you'd have to be doing something wrong to perform worse than the baseline Microsoft gives you.)