What happened

A bullish buy rating from investment bank Citigroup sent shares of electric car stock Lucid Group (LCID 2.57%) flying Thursday morning. And yet, electric truck start-up Rivian's (RIVN 2.81%) stock is doing pretty well today, too, rising a solid 5% as of 12:40 p.m. ET -- despite the fact that Citigroup didn't say one kind word about Rivian.

What's up with that?

Rivian R1T electric truck.

Image source: Rivian.

So what

In its note out on Lucid stock today, Citigroup explained that it likes the company's "best-in-class blend of range, performance, charging dynamics, and price" and considers Lucid -- which is coming to the EV market literal years behind market leader Tesla -- "still early to the premium EV market."  

Rivian, of course, is coming to the EV market at basically the same time as Lucid is. What's more, Rivian appears to have a sizable sales lead over its rival when it comes to vehicle preorders.

Consider: At last report, Lucid said it had amassed some 17,000 preorders for various trim levels of its new Lucid Air electric sedan. That's cute, reply Rivian investors -- because at last report, Rivian had racked up 71,000 (same digits, different order) preorders for its R1T electric trucks and R1S electric SUVs.

And Rivian has an Amazon order for 100,000 electric delivery vans in the bag. (And if analysts at Morgan Stanley are to be believed, that van order is only going to get bigger, reaching perhaps as many as 300,000 units by 2025).

Now what

That's a lot of EV preorders -- a lot more than Lucid has, at any rate. And it's here I think we find the answer to why investors are bidding up shares of Rivian today, on good news that's mainly just about Lucid.

Both Lucid and Rivian are what Citigroup gently describes as "pre-revenue" companies, meaning they not only have no profits -- they don't have any revenues to value them on! That quibble didn't dissuade Citi from recommending that investors buy Lucid stock this morning, however, and considering how much bigger Rivian's preorder pipeline is, it stands to reason that if Citi likes Lucid stock, then it should probably absolutely love Rivian stock.

Granted, Citi does admit that it thinks Lucid is a "high-risk" stock as well as a potential growth stock -- and if that's true for Lucid, it should be just as true for Rivian. 

If Lucid is a buy, then Rivian should be one, too.