Firstly 5i shows institutional holdings at 1.02% while several other site show it at over 70%, that's quite a discrepancy.
Secondly when one sees heavy volume trading it is assumed that it is the institutions moving the stock. With a sharp drop it is assumed that they are selling. My question would be who are they selling to?
Our data comes from a third party service. Some sites only report reported fund holdings, and some errors in timing are certainly possible as not all funds report in a timely manner. Some exclude insider shares in their percentage calculations. TFII does seem off, as Bloomberg shows 87%. There are always buyers on every single trade. Typically with high volume they are other institutions. We like to look at average trade size. Last week, for TFII, it was only 130 shares. This implies, but does not prove, that it was more individual trades on the buy sides vs institutions.