These two pipelines have very different operational histories so the simultaneous formation of a 'methane hydrate plug' in both pipelines seems highly unlikely at best. There's also no apparent reason why such a methane hydrate plug should cause seismic-scale explosions in both pipelines.

As far as motivation, the US agenda on Europe's fossil fuel market since at least 2008 has been to lock out Russian suppliers (who don't bank their oil profits with Wall Street) in favor of American and Middle Eastern importers (those who do bank their funds appropriately, i.e. Qatar/Saudi/Kuwait/UAE good, Iran bad). This has gained extra impetus since the fracking boom and the rise in production in the USA, leading to pushes to open up export markets.

Now, would Russia want to blow up its own pipelines when it can simply shut them down for 'maintenance' until sanctions are lifted if it wanted to cut off the flow of gas? That's a ludicrous stretch of the imagination. This leaves the USA as the one with the obvious motive to do this.

I personally think Europe would have been better off pushing rapid renewable development for the past few decades, which it has to some extent, but a more concentrated effort over the past few decades would have put them in a position where their economies were not dependent on either the USA or Russia.

[edit: relevant quote - "There are many ways to light Europe" - from the movie, Syriana]