When Marx and Engels assert that All that is solid melts into air in the world created by bourgeois capitalism what do they mean?

It means that it will basically self destruct, however my sociology professor states that the 'all that is solid melts into air' is a mis translation and that what Marx actually says is Alles Ständische und Stehende verdampft which translates to 'everything standing turns into steam'.

Meaning, Marx wasn't really going on about the ultimate downfall on the capitalist system but was making reference to (at the time of his writing) the introduction of the steam train and the locomotive revolution.