I just mean that by optimizing your app for AWS Lambda and using surrounding services like DynamoDB, S3, API Gateway, etc. it can/may be hard to later on move your app to some other platform.
For example, if you would instead split your app up in multiple docker containers, using open source technologies like expressjs, postgres and ngnix, it should be quite easy (or at least easier) to move your app to another platform which supports containers.
To be clear, I'm not saying that you shouldn't use AWS Lambda at all, just don't blindly follow the hype and carefully evaluate if it solves a problem you're having.