I don’t think so. Iirc, there is no sanction against Russian tanker ships, the sanction is on the Russian oil they carry. I’m no expert on maritime law, but I raising the Russian flag puts it under the auspices of the Russian government, so Russia has the right defend it under international law (it had a submarine escort) and lay claims against crimes against the vessel. It makes capturing the vessel a choice to get into a (additional) political entanglement with Russia.

This incident may also have implications to the convention of freedom of navigation . I don’t know. Again: not an expert