In a nutshell, that article speculates an US P8, that was tracked via public flight trackers attacked the pipeline with air dropped Mk54 torpedoes.
A couple thoughts about that:
- Torpedoes try to reject sea floor clutter, because that can interfere with their targeting of enemy vessels. If I had to guess, a Mk54 is about as inclined to attack a pipeline on the sea floor as an AMRAAM is inclined to attack a railway bridge. That doesn't mean that its impossible to build a torpedo that works for that, but one would have to justify the extra capability to the bean counters. There are all kinds of secret capabilities, so this clearly can't be ruled out, but the only reference to attacking the sea floor with torpedoes that I found on a very cursory search was a bug report about a misbehaving computer game.
- The Mk54 warhead is equivalent to roughly 100kg of TNT. A bit short of the reported hundreds of kg, but the accuracy of the seismic estimation is surely limited.
- A Mk54 torpedo will leave identifiable debris, making the attack attributable. Edit: It might also show up on passive acoustic surveillance systems, that monitor submarine activity.
- Civilian flight trackers can only track cooperative planes that provide their location via ADS-B, Mode S, UAT etc. This is a legal requirement for most civilian flights, but not for military flights. If one checks adsbexchange.com and filters for military aircraft, one can see that NATO is willing to disclose transport aircraft, tankers and surveillance aircraft close to the Ukrainian border, but outside of some limited locations in Western Europe, the combat aircraft stay in the dark. Military aircraft are also known to transmit false ADS-B information on occasion. If the P8 was tracked as claimed for even part of its flight, this means it was fully willing to be tracked.
1 + 2 are technical aspects that imho make it less likely, but they can't be used to rule out anything. 3 + 4 would imply that the US openly admits responsibility.
Reinhard