Three years ago I was working as the lead developer at a small startup in Europe, and a US competitor got in contact with the CEO and wanted to discuss an investment in us. The CEO told me to jump on a call and explain to them how our tech worked. I asked the CEO if they'd signed any form of NDA. Eventually they talked to our investors and they wrote to the company and asked to discuss an NDA. The company's reply was "We'd prefer to proceed without an NDA". I mean, no surprise there, I'm sure they would! We insisted on an NDA, no discussions were had.
To pretend to be interested in a collaboration and use that to steal another company's ideas is totally normal in our industry it seems.
Most startups are desperate and strap for cash. Added to the fact, they don’t have a lawyer on payroll, makes it a easy target for abuse.