  Lyman Break Galaxy (LBG) candidates at z>10 are rapidly being identified in
JWST/NIRCam observations. Due to the (redshifted) break produced by neutral
hydrogen absorption of rest-frame UV photons, these sources are expected to
drop out in the bluer filters while being well detected in redder filters.
However, here we show that dust-enshrouded star-forming galaxies at lower
redshifts (z<7) may also mimic the near-infrared (near-IR) colors of z>10 LBGs,
representing potential contaminants in LBG candidate samples. First, we analyze
CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but
detected at longer wavelengths. Combining the JWST data with (sub)millimeter
constraints, including deep NOEMA interferometric observations, we show that
this source is a dusty star-forming galaxy (DSFG) at z~5.1. We also present a
tentative 2.6sigma SCUBA-2 detection at 850um around a recently identified z~16
LBG candidate in the same field and show that, if the emission is real and
associated with this candidate, the available photometry is consistent with a
z~5 dusty galaxy with strong nebular emission lines despite its blue near-IR
colors. Further observations on this candidate are imperative to mitigate the
low confidence of this tentative submillimeter emission and its positional
uncertainty. Our analysis shows that robust (sub)millimeter detections of
NIRCam dropout galaxies likely imply z=4-6 redshift solutions, where the
observed near-IR break would be the result of a strong rest-frame optical
Balmer break combined with high dust attenuation and strong nebular line
emission, rather than the rest-frame UV Lyman break. This provides evidence
that DSFGs may contaminate searches for ultra high-redshift LBG candidates from
JWST observations.
