Here's the relevant part:
"sometimes people also like to play with mixed metaphors. It can be a fun way to turn a cliché on its head. For example, I’ve seen people mix the metaphors “Let’s cross that bridge when we come to it,” meaning let’s put off the decision, and “Don’t burn your bridges” meaning don’t destroy a something you’ll need later. They get “We’ll burn that bridge when we come to it,” which combines the meaning of the two metaphors into something like “We’re ready to fight when the right time comes,” and still maintains imagery that makes sense."
"We’ll burn that bridge when we come to it" seems to be considered a mixed metaphor, rather than anything more exotic.
Here's the relevant part: "sometimes people also like to play with mixed metaphors. It can be a fun way to turn a cliché on its head. For example, I’ve seen people mix the metaphors “Let’s cross that bridge when we come to it,” meaning let’s put off the decision, and “Don’t burn your bridges” meaning don’t destroy a something you’ll need later. They get “We’ll burn that bridge when we come to it,” which combines the meaning of the two metaphors into something like “We’re ready to fight when the right time comes,” and still maintains imagery that makes sense."
"We’ll burn that bridge when we come to it" seems to be considered a mixed metaphor, rather than anything more exotic.