No it's not.
Step 2: You buy shares in the company
Step 3: You publicly disclose you will buy the company, driving it's share price up
Step 4: You sell those existing shares now that the price has gone up.
That is trading on insider information.
If you have an intention to actually buy and make a good faith effort and fail, that's just business.
Elon is. He bought shares, then put in an offer which drives his existing shares up. Perhaps you can argue until he sells them he isn't acting.. perhaps.. but if he sells them today, are you still telling me he isn't acting on insider information?
A principal shareholder is a person that directly or indirectly owns or controls more than 10% of any class of voting shares or securities of a company. The principal shareholder has the authority to vote using those voting shares.
Elon has less than 10% share (9.2%), so he's not an insider. Probably he stayed under 10% because of this law.
Unless you think he just woke up today and said: You know what, I'm going to buy Twitter! Which, I mean.. given Elon maybe that's what happened. But if it was premeditated then he has clearly been acting on insider information.