The rest of Mei's response is a predictable part of her personality. I'm not surprised by her personality after all this time. She has her quirks but it's noticeable when she's making an attempt to be "softer." For someone else that might be dry but for her it reads a bit different. She'll always be like that.
Your lack of surprise at Mei’s personality is neither here nor there. Mei now reads as even colder and more distant when interacting with Yuzu than she has in the past, and certainly more so than in the original series. I see this as less a function of the supposed psychology of Mei the imaginary human and more about Saburouta’s current perfunctory approach to characterization—Yuzu shall be warm and bubbly while Mei is reserved and emotionally distant in order to show the contrast between them, and thus it shall ever be.
For every instance of Mei acting proactively affectionate toward Yuzu in Citrus+ we have had exponentially more scenes of Mei scolding Yuzu, putting her in her place, telling her that she should be doing or feeling something other than what she is doing or feeling (as happens here), or generally behaving as an authority figure (employer or strict older relative) rather than as a partner in a romantic relationship.
Readers desperate for some slight sign of actual intimacy between the MCs are free to read “softness” into Mei’s minimal and ambiguous facial expressions, of course.