Panel 1: Since John doesn't do something stupid like "phone and tell Elly he'll be late", we find her serving out supper being Mrs Exposition and wondering where he is because he's not usually late for his indigestible supper and hopes that nothing is wrong.
(It should be noted that her idea of wrong is more along the lines of 'cheating on her with either another woman or with a better cook' and less 'wrapped around a telephone pole'.)
Panel 2: Liz suggests that perhaps he's been held up by a late patient while Mike says that he could be stuck in rush hour traffic.
Panel 3: As we look at John and Jasper laughing like the idiot children Lynn thinks model railroaders are because they play with toys, Mike also thinks that Dad could be held up by a real train.
Summary: Lynn really never quite understood what Rod is doing with his trains and never really wanted to. All she sees is a toy and assumes that he wants to be a stupid kid getting in her way and being as selfish and dumb as a kid.