As @MrGeneric mentions, it’s because it’s tying back to the prior sentence.
Looking at this again on a new day, and freshly reading only the one さすがに word balloon in isolation, I completely understand the interpretation of “Sure enough, (they would go) somewhere like toward the station.”
If we extend our scope a bit, here’s what takes place:
In the first panel, Yui establishes the topic as 範囲 (range). While は and も are the primary ways to establish a topic, because the topic is simply what one is talking about, the (indirect) quote marker って works to establish a topic as well. That’s what we have here (「そういえば、範囲ってどこまでなんだろう」), as she wonders what the range of hiding is.
The second panel doesn’t have a topic specified, as it’s carrying over the same topic of 範囲. She’s still commenting on the range, as she considers that they should have established it in advance, what the range would be.
Going into the third panel, she’s still talking about the same thing, 範囲, the range. Here, she’s saying the others wouldn’t go outside of the park. In Yui’s mind, this establishes the range as within the limits of being inside of the park.
Still in panel three, she then introduces a new topic: 「駅の方とか」. Now she’s talking about a location outside what she believes to be the sensible range for hiding, and her comment is さすがに. This means that going somewhere like the station is as Yui expects. That expectation is what she figured in the prior word balloons: the range of the game is within the park, and therefore something like the station is sure enough, outside of bounds, as she’s figured.
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