The highest recorded temperature for extreme thermophiles, growing at the very edge of undersea vents is about 400oC. The commonly cited lowest temperature for lava is 700oC. Given a fudge factor on both of these, it is conceivable that there could be an overlap. I doubt if such an event would occur: the underseas vents last for a long time and bacteria have had ample opportunity to adapt/evolve. Molten lava is very short lived, so there would be no time or reason for the bacteria to use it as a habitat.
So, to claim that 'bacteria can live in lava', may be better described as 'could possibly survive',