Hi. Yes. The phrase, "I though that you were toast" implies that the speaker thought that Jackson had died. It could be further implied that Jackson died by way of fire (i.e. from the volcanic action), because toast is made (browned, cooked) by way of heat and flames. Another example of the term "toast" as it was used in the movie could be as follows: "Judy didn't study for the final. She's toast! " This means that she didn't study, and as a result she is going to fail (i.e. be consumed as if by fire by the test)