When something is stolen, the original owner no longer has posession of the stolen object. If the story were about money or physical property, "stealing" would be appropriate. It is not.
The word "copying" is quite adequate. In this case, direct copying is obviously poor behaviour. It betrays a lack of capability on the part of the copyer. This story would have had the same emotional impact, had it used the correct term.
Using the word "stealing" mires the story in the intricacies of digital copyright debate, which is not what this is about. It is about a startup not doing its own work, and thus demonstrating inability.
1. You come home from work, and find that while you were gone someone came into your garage and stole your motorcycle.
It would be quite normal to exclaim "I've been robbed!". Yet you in fact have been burgled, not robbed. Nevertheless in common English usage people use "robbed" in a more expansive sense than it is use in law. If writing a police report, or an indictment, one must make the distinction, but not in regular conversation.
2. You are in a bar, in a tuxedo, obviously trying to drink yourself into oblivion. I ask you what is wrong. You tell me "my best friend stole my fiancé...on our wedding day!".
Technically, he did not steal her, as she is not property. He perhaps committed tortious interference with contract, or maybe alienation of affection. However, if you are not writing the pleadings for a lawsuit, it is in fact perfectly acceptable to say the bastard stole your fiancé.
3. You are the quarterback for your high school football team. The big game is coming up with your most hated rival high school. Your sister starts dating the quarterback of their time. While he is at your house visiting your system, he sneaks into your room, where you have your team's confidential playbook. He quickly uses his cell phone camera to take photos of each page.
This would generally be described as him stealing your plays, even though it is not legally stealing (and probably isn't even legally a crime).
The use of terms like stealing, theft, robbery, and so on to describe situations where they do not literally apply in the legal sense goes back a long way. E.g., from Shakespeare: "Who steals my purse, steals trash, but he that filches from me my good name robs me of that which not enriches him and makes me poor indeed." Note that he is using both filching (a synonym for stealing) and robbery to describe damaging a reputation.
Copyright law's mechanism is to create a property interest in the right to make and distribute copies of a given work. Exercising someone else's property interests without there permission is acceptably called "theft" in ordinary English.