By "reliable" it sounds like you mean "legitimate"? As in, $asn is "authorized" to announce $prefix? "originAS" exists for that purpose.

Also, it's not clear what they're (ipinfo.io) using as their source for the ASN. Are they simply reporting the ASN as provided by ARIN, etc., or are they actually running BGP and reporting the origin ASN as they see it in announcements. My money would be on the former, in which case any prefix hijacking would not affect the data reported by ipinfo.io.